This invention relates to a crushable heater core for an electric heater device, a compacted unitary electric heater device, and a method for making such devices. Such devices include, without limitation, swaged sleeve heaters, often in a hollow tube-like configuration, for delivering or processing material, such as plastic or other molten material, within or exterior to such a tube-like structure, for forming plastics, food processing, packaging, glue or other dispensing operations, in aerospace, liquid metal transfer, die casting, chemical, liquid processing, glass processes, gas heating equipment and other processes where close control is required. Such heaters can be constructed with sheaths of tool or stainless steel, super alloys and other critical materials, and may have special purpose coatings where required.
Heater devices embodying the present invention offer heat transfer and performance characteristics and superior dielectric properties not found in conventional devices. The construction and design of such novel devices permit easy and effective control and performance enhancement, and may be constructed with distributed wattage, multiple independent heat zones, one or more integral thermocouples and singular or multiple thermowells which may accommodate sheathed, mineral insulated thermocouples for easy insertion or removability.
Devices embodying the present invention utilize a novel cylindroid crushable crushable ceramic core which has key hole shaped grooves on its interior surface for receiving lead pins in communication with a winding of electric heating wire, and the wound core is entrained in upper and lower sleeves and swaged to provide electrical contact between the lead pins and the heater element wire.
The unique heating element embodying the present invention starts with one or more novel crushable ceramic core(s) of special configuration. Such core(s) comprises a cylindroid or cylinder which is fabricated with key hole shaped longitudinal grooves along their internal circumferential periphery. The entry to a groove comprises a keyhole like slot which is narrower at its entry and enlarged as it enters the circumferential wall of the cylindroid or cylinder. This keyhole slot may have a cross section which is rectangular or oblong or pillow shaped as long as its interior is of greater cross-section than its keyhole entry.
The crushable ceramic core or cores are wound with heating element wire. The wire windings can be spaced as to provide distributed wattage, or cold zones on each core. The lead and terminal ends of the heating element wire are threaded into the cores in alignment with selected key slots. Selected alternate key slots in one or more cores of a multi-core assembly permits creation of independently powered cores to provide independently heated zones. Unwound cores can be placed at the ends of the core assembly or between multiple cores to provide additional cold zones to meet application or lead termination needs.
A conductive pin having a cross section substantially conforming to the cross section of a key slot is slid into each groove having a heated wire end intersection with the groove, so that a pin and wire end contact one another.
If thermowells for use with separate thermocouple sensors or thermocouple wires to create sensors for heat control are desired, they may be installed in one of the grooves.
The interior of the wire wound ceramic core and arranged pin assembly is slid into a first tube like or solid metal sleeve and within a second outer metal sleeve so that the wire wound ceramic core and arranged pin assembly is sandwiched between the first and second metal sleeves. Preferably, the first inner sleeve is sized to accommodate the wire wound ceramic core to permit easy sliding of the core into place.
Magnesium Oxide or similar insulating power is poured into the space between the core and the sleeves and the assembly is vibrated until the space between the parts is full and compacted to the extent possible by vibration.
A tool rod or tube is inserted into or over the inner tube-like or solid sheath sleeve, and the assembly is inserted into a swaging machine and subjected to circumferential hammering until the outer diameter of the assembly is reduced to a size which compacts the internal ceramic core and insulating ceramic powder to near theoretical maximum density so that the connection between each of the pins and its associated element wire end is substantially unitized for effective electrical connection and that the ceramic powder in the key slots between the pin and the inner sleeve is compacted to provide the required electrical insulation properties between the pin and inner tube-like or solid metal sleeve.